COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Piper PA-23 (Apache and Aztec) Series Aeroplanes AD/PA-23/55 Fuel System - Inspection and Modification 11/72 Applicability: All PA-23 series with S/N 27-1 to 27-2504 and 27-2505 to 27-4765. Document: Piper SL No. 606A. Compliance: At next major inspection after 30 November 1972.